Cloud Computing & ROI - Realistic/Practical Expectations

The Delaware Valley chapter of the Cloud Security Alliance (CSA-DelVal) is hosting a roundtable on Wednesday, May 18th to discuss many concerns, such as what is a practical/realistic expectation regarding the ROI for cloud computing. I believe the research data is not there yet, but it is only a matter of time before Gartner/Forrester, etc. come up with some numbers. What % are you expecting (for using a private/public cloud)?